At least one species of teleost fish has now been shown to use a form of echolocation to detect the presence of nearby obstacles. The sea catfish, Arius felis, produces low frequency sound pulses that function in social communication. In addition, the reflections and reverberations of these sounds assist in detecting obstacles in the immediate area. This function is enhanced by the directional receiving and sound projecting qualities of the swim bladder. Electrophysiological evidence shows that the lateral line system has an important role in directional near-field detection. The range and accuracy of this system will be investigated, particularly under open water conditions. In this species, the male incubates the eggs and embryos up to hatching, and the feasibility of using and maintaining embryos and hatchlings is being investigated. The purpose of this is an investigation of the development of the sonic behavior in the species, both in terms of the social communication and echolocation functions. The echolocating mechanisms in this species are considered relatively simple and primitive, as compared to those of bats and dolphins, and, as such, should provide significant information for the study of other simple echolocating systems, such as those that can be developed in humans.